Tunable Nonreciprocal Tunneling Based on Nonsymmetric Magnetoplasmonic Resonance Structure

In order to achieve nonreciprocal transmission, we design an optical system composed of a sandwiched structure (magneto-optical media/metal/magneto-optical media) and a pair of coupling prisms. Using the developed transfer matrix method for magnetic materials, we study the transmission properties of the system in detail. The unusual result is that a tunable nonreciprocal resonance tunneling can be achieved through a nonsymmetric configuration of the system. The nonreciprocal resonance tunneling results from the nonsymmetric coupling of magnetoplasmonic coupled resonances. The results are verified through an electromagnetic field simulation based on the finite element solver.     

A genetic screen for increased loss of heterozygosity in Saccharomyces cerevisiae

Loss of heterozygosity (LOH) can be a driving force in the evolution of mitotic/somatic diploid cells, and cellular changes that increase the rate of LOH have been proposed to facilitate this process. In the yeast Saccharomyces cerevisiae, spontaneous LOH occurs by a number of mechanisms including chromosome loss and reciprocal and nonreciprocal recombination. We performed a screen in diploid yeast to identify mutants with increased rates of LOH using the collection of homozygous deletion alleles of nonessential genes. Increased LOH was quantified at three loci (MET15, SAM2, and MAT) on three different chromosomes, and the LOH events were analyzed as to whether they were reciprocal or nonreciprocal in nature. Nonreciprocal LOH was further characterized as chromosome loss or truncation, a local mutational event (gene conversion or point mutation), or break-induced replication (BIR). The 61 mutants identified could be divided into several groups, including ones that had locus-specific effects. Mutations in genes involved in DNA replication and chromatin assembly led to LOH predominantly via reciprocal recombination. In contrast, nonreciprocal LOH events with increased chromosome loss largely resulted from mutations in genes implicated in kinetochore function, sister chromatid cohesion, or relatively late steps of DNA recombination. Mutants of genes normally involved in early steps of DNA damage repair and signaling produced nonreciprocal LOH without an increased proportion of chromosome loss. Altogether, this study defines a genetic landscape for the basis of increased LOH and the processes by which it occurs.     

Paul Drude's Prediction of Nonreciprocal Mutual Inductance for Tesla Transformers

Inductors, transmission lines, and Tesla transformers have been modeled with lumped-element equivalent circuits for over a century. In a well-known paper from 1904, Paul Drude predicts that the mutual inductance for an unloaded Tesla transformer should be nonreciprocal. This historical curiosity is mostly forgotten today, perhaps because it appears incorrect. However, Drude''s prediction is shown to be correct for the conditions treated, demonstrating the importance of constraints in deriving equivalent circuits for distributed systems. The predicted nonreciprocity is not fundamental, but instead is an artifact of the misrepresentation of energy by an equivalent circuit. The application to modern equivalent circuits is discussed.     

Perfect Nonreciprocal Absorption Based on Metamaterial Slab

Plasmonics - In order to achieve nonreciprocal absorption, we design a metamaterial slab made of arrays of tilted metal layers. Through studying the extraordinary material dispersion, we derive the...     

Luminescence investigation of a cerium‐doped yttrium vanadate phosphor

Cerium (Ce³⁺)‐doped (1, 3, and 7 mol%) yttrium vanadate phosphors were prepared using a co‐precipitation technique. The structural and optical properties of the synthesized samples were studied using X‐ray diffraction (XRD), Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HR‐TEM), optical absorption, and photoluminescence (PL) spectroscopy techniques. The tetragonal structure and the formation of the nanosized crystallites in the YVO₄:Ce phosphor were confirmed using XRD analysis. HR‐TEM morphology showed rod‐like nanoparticles of different sizes. Optical absorption spectra demonstrated strong absorption bands at 268 and 276 nm. PL spectra showed strong peaks at 546, 574, and 691 nm following excitation at 300 nm. The calculated CIE chromaticity coordinates demonstrated that YVO₄:Ce could be used as a novel phosphor for the development of light‐emitting diode lamps.     

Electronic structure of boron-doped finite graphene sheets: unrestricted DFT and complete active space calculations

B3LYP and complete active space methods were applied to study graphene nanoribbons (GNRs) doped with boron atoms. The restricted B3LYP solutions were found to be unstable in all but two cases, and the complete active space calculations prove the multiconfigurational character of the ground state contributing with two most important configurations. The exception is the structure c4 where the system has single reference ground state in spite of the instability of the restricted wavefunction.

The distance between dopant atoms, their mutual position and their location within the nanoribbon impact the relative stability of doped nanoribbons. B doping does not modify the ionisation potentials of doped GNRs. However, it notably increases the electron affinity of the core-doped nanoribbons. The doping also has a notable impact on the reorganisation energy of the nanoribbons. The reorganisation energy of B-doped GNRs is higher than the corresponding reorganisation energy of pristine and nitrogen-doped GNRs.     

Modification of CETP function by changing its substrate preference: a new paradigm for CETP drug design

We previously determined that hamster cholesteryl ester transfer protein (CETP), unlike human CETP, promotes a novel one-way transfer of TG from VLDL to HDL, causing HDL to gain lipid. We hypothesize that this nonreciprocal lipid transfer activity arises from the usually high TG/cholesteryl ester (CE) substrate preference of hamster CETP. Consistent with this, we report here that ∼25% of the total lipid transfer promoted by the human Q199A CETP mutant, which prefers TG as substrate, is nonreciprocal transfer. Other human CETP mutants with TG/CE substrate preferences higher or lower than wild-type also possess nonreciprocal lipid transfer activity. Mutants with high TG/CE substrate preference promote the nonreciprocal lipid transfer of TG from VLDL to HDL, but mutants with low TG/CE substrate preference promote the nonreciprocal lipid transfer of CE, not TG, and this lipid flow is in the reverse direction (from HDL to VLDL). Anti-CETP TP2 antibody alters the TG/CE substrate preference of CETP and also changes the extent of nonreciprocal lipid transfer, showing the potential for externally acting agents to modify the transfer properties of CETP. Overall, these data show that the lipid transfer properties of CETP can be manipulated. Function-altering pharmaceuticals may offer a novel approach to modify CETP activity and achieve specific modifications in lipoprotein metabolism.     

Nanoantenna-Assisted Extraordinary Optical Transmission Under Radial Polarization Illumination

We numerically study the extraordinary optical transmission of a plasmonic structure that combines a circular nanoantenna and a vertical annular nanoslit etched into a gold film under radially polarized illumination. The nanoantenna collects the incident field and localizes it in a horizontal Fabry-Pérot cavity over the gold film. The vertical nanoslit positioned at the maximal field in the horizontal cavity couples the localized field and facilitates its transmission to the free space. Due to the symmetry matching between the structure and the illumination polarization, surface plasmons can be excited effectively and enhance the transmission. Through optimizing the structure parameters, the transmission efficiency can be greatly enhanced by 225 times for a resonant annular nanoslit and 251 times for a non-resonant annular nanoslit. This axisymmetric extraordinary optical transmission setup may be fabricated on the facet of an optical fiber for optical sensing applications.     

Age-related parameters of spinal inhibition of skeletal muscles in regulation of voluntary movements in men

Age-related features of spinal inhibition in the regulation of voluntary movements in men were studied. It was found that presynaptic and nonreciprocal and reciprocal inhibitions of the flexor of toes during voluntary movements were less intense than inhibition during relative muscle rest in subjects of all age groups. This results from the age-related features of supraspinal excitatory and inhibitory effects on Ia and Ib spinal interneurons, which change the mechanism of spinal inhibition of voluntary movements as the organism develops. In boys 9–12 years of age, execution of voluntary movements is accompanied by the lowest presynaptic inhibition of Ia afferents and the most pronounced increase in nonreciprocal and reciprocal inhibition of α-motoneurons in the flexor of toes, compared to the other age groups. Execution of voluntary movements by boys 14–15 years of age leads to an increase in presynaptic inhibition of Ia afferents and the most pronounced decrease in reciprocal and nonreciprocal inhibition of spinal α-motoneurons of the flexor of toes. By the age of 17–18 years, the mechanism of nonreciprocal inhibition of α-motoneurons of the flexor of toes during voluntary movements is similar to that in adolescents aged 14–15 years. The definitive level of presynaptic inhibition of Ia afferents and reciprocal inhibition of α-motoneurons of the flexor of toes during voluntary movements is reached by 17–18 years.     

Unidirectional Absorption in a Three-Dimensional Tunable Absorber Under Oblique Incidence

Plasmonics - In this paper, we propose a three-dimensional tunable absorber to realize a controllable unidirectional absorption and unidirectional transmission based on the plasma metamaterial,...     

Unidirectional Gene Conversion Associated with Two Insertions in NEUROSPORA CRASSA Mitochondrial DNA

The mitochondrial phenotype of [poky] and other extranuclear Neurospora mutants is known to predominate over that of wild type in heteroplasmons. In the present work, we have investigated the interaction between wild-type and [poky] mtDNAs using as many as four physical markers to distinguish the two types of mtDNAs. Two insertions, one of 1200 bp in Eco RI-5 and the other 50 bp in Eco RI-9, are identified as sites of high frequency, unidirectional gene conversion leading to their spread through mtDNA populations in heteroplasmons. However, the transmission of the [poky] mutation does not appear to be correlated with the transmission of either of these insertions or of other physical markers. The possibility that other loci of nonreciprocal recombination might be responsible for the "dominance" of Neurospora extranuclear mutants is discussed.     

Broadband Terahertz Absorption in Graphene-Embedded Photonic Crystals

The absorption in graphene is rather low at terahertz frequencies. Here, we present a graphene-embedded photonic crystal structure to realize broadband terahertz absorption in graphene. The approach provides absorption enhancement in the whole terahertz regime (from 0.1 to 10 THz). It is shown that the average absorption in the graphene-embedded photonic crystal can be enhanced in the multiple propagating bands of the photonic crystals. The absorption efficiency can be further improved by optimizing the characteristic frequency, optical thickness ratio in a unit cell, and the angle of incidence on the photonic crystals. A maximum broadband absorption factor of 28.8% was achieved for fixed alternative dielectric materials. The graphene-embedded photonic crystal is promising for terahertz functional devices with broadband response.     

Theoretical and experimental investigation of doping M in ZnSe (M = Cd,Mn, Ag,Cu) clusters: optical and bonding characteristics

The optical and bonding characteristics of doping ZnSe quantum dots (QDs) were investigated. Cd‐, Mn‐, Ag‐ and Cu‐doped ZnSe were synthesized in aqueous solution. Theoretically, the intensity of the Cd–Se bond was similar to that of the Zn–Se bond, which illustrates that Cd can be doped into ZnSe materials at any ratio. We found that Mn–Se bonding was stronger than Zn–Se bonding. Ag‐doped ZnSe nanoclusters show the same bonding and configuration as Cu‐doped ZnSe. Moreover, Cd can be doped into ZnSe using both the substitution‐ and vacancy‐doping method. For Mn‐doped ZnSe clusters, small amounts of Mn impurity lead to stronger bonding with Se, but larger amounts of Mn impurity led to the formation of a Mn–Mn metal bond. The theoretical results show that it is difficult to form a vacancy‐doping cluster for Mn‐doped ZnSe materials. In experiments, the absorption and photoluminescence (PL) spectral wavelengths of Mn‐doped ZnSe nanocrystals were the same as those of pure ZnSe nanocrystals, showing that the Mn impurity is not doped into ZnSe nanocrystals. Ag‐ and Cu‐doped ZnSe nanocrystals have the same PL characteristics. The doping of an impurity is related to the solubility product, and not the bonding intensity. Copyright © 2015 John Wiley & Sons, Ltd.     

Cell science and protein crystal growth research for the International Space Station

The recent National Research Council report, Future Biotechnology Research on the International Space Station, evaluates NASA's plans for research in cell science and protein crystal growth to be conducted on the International Space Station. This report concludes that the NASA biotechnology programs have the potential to significantly impact relevant scientific fields and to increase understanding and insight into fundamental biological issues. In order to realize the potential impacts, NASA must focus its research programs by selecting specific questions related to gravitational forces' role in cell behavior and by using the microgravity environment as a tool to determine the structure of macromolecules with important biological implications. Given the time and volume constraints associated with space-based experiments, instrumentation to be used on the space station must be designed to maximize the productivity of researchers, and NASA's recruitment of investigators and support for space station experiments should aim to encourage and facilitate cutting-edge research.     

Plasmonic Control of Refractive Index Without Absorption in Metallic Photonic Crystals Doped with Quantum Dots

Plasmonics - We investigate the refractive index without absorption in metallic photonic crystals doped with quantum dots. It is found that the absorption and dispersion of probe field can be...     

Facile Metal Coordination of Active Site Imprinted Nitrogen Doped Carbons for the Conservative Preparation of Non‐Noble Metal Oxygen Reduction Electrocatalysts

Iron‐ or cobalt‐coordinated heteroatom doped carbons are promising alternatives for Pt‐based cathode catalysts in polymer‐electrolyte fuel cells. Currently, these catalysts are obtained at high temperatures. The reaction conditions complicate the selective and concentrated formation of metal–nitrogen active sites. Herein a mild procedure is introduced, which is conservative toward the carbon support and leads to active‐site formation at low temperatures in a wet‐chemical metal‐coordination step. Active‐site imprinted nitrogen doped carbons are synthesized via ionothermal carbonization employing Lewis‐acidic Mg²⁺ salt. The obtained carbons with large tubular porosity and imprinted N₄ sites lead to very active catalysts with a half‐wave potential (E_1/2) of up to 0.76 V versus RHE in acidic electrolyte after coordination with iron. The catalyst shows 4e^? selectivity and exceptional stability with a half‐wave potential shift of only 5 mV after 1000 cycles. The X‐ray absorption fine structure as well as the X‐ray absorption near edge structure profiles of the most active catalyst closely match that of iron(II)phthalocyanine, proving the formation of active and stable FeN₄ sites at 80 °C. Metal‐coordination with other transition metals reveals that Zn–N_x sites are inactive, while cobalt gives rise to a strong performance increase even at very low concentrations.     

Electrochemical CO2 Reduction with Atomic Iron‐Dispersed on Nitrogen‐Doped Graphene

Electrochemical reduction of CO₂ provides an opportunity to reach a carbon‐neutral energy recycling regime, in which CO₂ emissions from fuel use are collected and converted back to fuels. The reduction of CO₂ to CO is the first step toward the synthesis of more complex carbon‐based fuels and chemicals. Therefore, understanding this step is crucial for the development of high‐performance electrocatalyst for CO₂ conversion to higher order products such as hydrocarbons. Here, atomic iron dispersed on nitrogen‐doped graphene (Fe/NG) is synthesized as an efficient electrocatalyst for CO₂ reduction to CO. Fe/NG has a low reduction overpotential with high Faradic efficiency up to 80%. The existence of nitrogen‐confined atomic Fe moieties on the nitrogen‐doped graphene layer is confirmed by aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy and X‐ray absorption fine structure analysis. The Fe/NG catalysts provide an ideal platform for comparative studies of the effect of the catalytic center on the electrocatalytic performance. The CO₂ reduction reaction mechanism on atomic Fe surrounded by four N atoms (Fe–N₄) embedded in nitrogen‐doped graphene is further investigated through density functional theory calculations, revealing a possible promotional effect of nitrogen doping on graphene.     

The effects of manganese doping on UVA absorption and free radical generation of micronised titanium dioxide and its consequences for the photostability of UVA absorbing organic sunscreen components.

The effect of manganese doping on the free radical generation rate, free radical scavenging and UVA absorption properties of micronised sunscreen grade titania has been studied with respect to enhancement of the UVA photostability of test sunscreen formulations containing the organic UVA absorber Parsol 1789. Manganese doping has been shown to increase the UVA:UVB absorption ratio of titania, reduce free radical generation rates by over 90%, and provide free radical scavenging behaviour. Adding manganese-doped titania to a test formulation incorporating Parsol 1789 shows that manganese doping increases UVA attenuation stability by up to 3 times the amount achieved by comparable commercial undoped titania materials. HPLC data shows this to be related to an improved stabilisation of the organic sunscreen components. Manganese doped titania shows improved efficacy over undoped titania in sunscreen formulations containing organic UV absorbers.     

Luminescence study on Mn,Ni co‐doped zinc sulfide nanocrystals

Zinc sulfide (ZnS) doped with transition metal has been used as phosphor for various optoelectronic applications. In the present report, ZnS:Mn doped and ZnS:Mn,Ni co‐doped were prepared using chemical co‐precipitation method using polyvinyl pyrolidone as a surfactant. The structural studies were carried out using an X‐ray diffraction technique; optical studies have been performed using ultraviolet–visible light absorption and photoluminescence (PL) spectroscopy. The presences of functional groups were confirmed using Fourier transform infrared spectroscopy. The X‐ray diffraction study and Reitveld analysis confirms the formation of cubic phase with crystalline size 2–3 nm for undoped and doped ZnS nanoparticles. A novel and enhanced luminescence characteristic have been observed in PL spectra. The luminescence intensity of Mn,Ni co‐doped ZnS in the blue region is much higher of that of ZnS. The PL results indicate that the doping of Ni creates shallow trap states or luminescence centres in the forbidden energy gap, which quenches the Mn states emission. Concentration quenching has been observed in Mn‐doped ZnS nanoparticles. From CIE coordinates, it is seen that the yellow and blue light emission of ZnS:Mn,Ni co‐doped nanophosphor may be a promising candidate for display devices and phosphor converted light‐emitting diode applications.     

Theoretical and experimental investigation of stability and spectra of doped Ag:ZnSe nanocrystals

In experiment, doped Ag:ZnSe nanocrystals (NCs) had better stability than that of ZnSe nanocrystals under ambient atmospheres in the presence of air and light illumination. However, it is difficult to explain the mechanism of better stability of Ag:ZnSe nanocrystals from the experiment perspective for doped nanocrystals are more unstable than corresponding pure nanocrystals in general. Using B3LYP/LANL2DZ method, we have investigated the geometrical structures, bonding characters, and molecular orbitals (MOs) of hexagonal and tetrahedral Ag doped ZnSe structures in theory. The results showed that the good stability of Ag:ZnSe nanocrystals can be attributed to the stronger binding between Ag and Se. Moreover, we have proved that Ag doped ZnSe nanocrystals synthesized in experiment should be substituting doped but not vacuity doped. Substituting Ag doped ZnSe molecules have the same configuration as that of the ZnSe structure, but vacuity doped Ag:ZnSe have completely different configuration than ZnSe structure due to the big size of Ag atom. In addition, through contrast of MO of ZnSe and Ag doped ZnSe, we have testified that Ag easily formed bonds with Se. The high binding energy and high probability of forming bonds with Se atom make Ag doped ZnSe nanocrystals have better stability than that of ZnSe nanocrystals.